Utility of a Novel Imaging Algorithm (4DX) for the Diagnosis of Constrictive Bronchiolitis

Constrictive (or obliterative) bronchiolitis is a rare pulmonary disease characterized by subepithelial inflammatory and fibrotic narrowing of the bronchioles on histologic analysis, which often presents with nonspecific symptoms such as progressive dyspnea on exertion and nonproductive cough over weeks to months. Constrictive bronchiolitis may be triggered by autoimmune disease, chronic allograft rejection in lung transplant recipients, graft versus host disease in stem cell transplant recipients, viral illness, or inhaled toxins. Although pulmonary function tests (PFTs) may be helpful for the diagnosis of constrictive bronchiolitis, a study performed by King and colleagues in 2009 found that many Veterans with biopsy-proven constrictive bronchiolitis had normal PFTs. Thus, for these patients, more sensitive methods of noninvasive testing are needed.

4Dx XV Ventilation Analysis is a new imaging analysis algorithm which utilizes standard fluoroscopy to quantify ventilation with sufficient fidelity to identify regional differences. Fluoroscopic images of a single tidal breath are obtained at 5 distinct angles (direct AP, +/- 36 degrees, and +/- 72 degrees). Readouts from the 4Dx XV Ventilation Analysis include absolute value of total lung ventilation, heterogeneity of lung ventilation, a frequency distribution of lung ventilation as a line plot, and a regional map of lung ventilation. In addition, an expiratory time constant (time to exhale 63% of the tidal volume), heterogeneity of the expiratory time constant, frequency distribution of expiratory time constant as a line plot, and a regional map of expiratory time constant are also calculated. Pilot studies performed by 4D Medical show data generated by the 4Dx XV Ventilation Analysis software applied to fluoroscopy is reproducible in individuals with normal lung function and the heterogeneity index increases in individuals undergoing radiation therapy.

The investigators hypothesize that the 4Dx XV Ventilation Analysis program, when applied to standard fluoroscopic images, is more sensitive for the diagnosis of constrictive bronchiolitis than PFTs in Veterans with constrictive bronchiolitis. Specific metrics that will be evaluated with the software include ventilation heterogeneity and expiratory phase constants, among other metrics. Endpoints will be compared during tidal breathing and a full exhalation to residual volume from functional residual capacity.